根据小信号的 Bespalov-Talanov理论 ,考虑光束的自由空间传输 ,计算了级联片状放大器小信号噪声的功率增益谱 ,通过比较不同参数的功率谱的变化 ,分析了影响功率谱强度及最大增益频率的因素。结果表明 ,以 B积分作为非线性自聚焦效应强弱的唯一判据是不够的 ,除了 B积分外 ,还应给出噪音的等级。对于级联片状放大器 ,考虑和不考虑光束的自由传输 ,极大增益的中心频率的差别很大 ,在空间滤波器小孔的截止频率的选择时必须考虑到这一点 According to the Bespalov-Talanov theory of small signal, considering the free space transmission of the light beam, the power gain spectrum of the small signal noise of the cascaded amplifier is calculated. By comparing the power spectrum changes of different parameters, the influence of the power spectrum intensity and the maximum gain Frequency factor. The results show that the integral of B is not the only criterion for the nonlinear self-focusing effect. In addition to B integral, the noise level should also be given. For cascaded amplifiers, the center frequency of the maximal gain varies greatly with or without considering the free transmission of the beam. This must be taken into account when choosing the cut-off frequency of the spatial filter aperture